I already have a CDN provider. Can I still use Cloudflare?

Yes, you can still use another CDN provider (CloudFront, MaxCDN, NetDNA, etc.) with Cloudflare to help speed up your site. You would just want to make sure that the CNAME for the CDN provider is included in your Cloudflare DNS settings. You can add the subdomain by going to:

Settings->DNS settings

Please note -- Certain CDN providers will not work if the DNS record is Orange Clouded (Cloudflare-enabled) and would instead result in 100X or connectivity errors, so if you don't see a cloud at all, then we've marked the record as not-proxiable.